The investigators will establish human primary cell cultures including keratinocytes, hepatocytes, and renal, mammary, cervical, bronchial, buccal, and prostatic epithelial cells. The cultures will be used to establish the 50% toxic dose based on endpoints of growth, differentiation, and appropriate surrogate biomarkers for 20 chemopreventive agents. The TD50 will be correlated to data derived from plasma and tissue analyses in preclinical and clinical studies.